The present invention relates to a continuous heat treatment of cold-rolled steel strip.
Heat treatment is particularly important for giving strip an excellent limit of elasticity combined with high elongation (at fracture) and homogeneity of properties throughout its width, which results in satisfactory drawability. Such qualities are particularly desirable for strip with high limit of elasticity used in the car industry.
When one wishes to obtain good ductility, drawability, and elongation in cold-rolled strip, the strip is generally subjected to coil recrystallization annealing in a bell furnace. Such treatment, however, is expensive because it is of long duration and thus of low productivity; moreover, the results attained with this treatment are quite variable. To remedy such inconveniences, it has already been suggested to replace such an annealing treatment with a continuous heat treatment. However, notwithstanding various suggested modifications, it is still impossible to obtain every time satisfactory homogeneity in the properties of the strip throughout its width and good ductility, while maintaining an acceptable treatment duration.